U.S. patent application number 13/872459 was filed with the patent office on 2014-07-03 for hearing aid with improved localization.
This patent application is currently assigned to GN ReSound A/S. The applicant listed for this patent is GN ReSound A/S. Invention is credited to Karl-Fredrik Johan GRAN, Guilin MA, Jacob Ulrik TELCS.
Application Number | 20140185846 13/872459 |
Document ID | / |
Family ID | 51017245 |
Filed Date | 2014-07-03 |
United States Patent
Application |
20140185846 |
Kind Code |
A1 |
GRAN; Karl-Fredrik Johan ;
et al. |
July 3, 2014 |
HEARING AID WITH IMPROVED LOCALIZATION
Abstract
A hearing aid includes: a cue filter having an input that is
provided with an output from the BTE sound input transducer; an
adaptive feedback canceller configured to provide an output
modelling a feedback path between the output transducer and the BTE
sound input transducer, wherein the output modelling the feedback
path is provided to a subtractor for subtraction of the output
modelling the feedback path from the output of the BTE sound input
transducer to obtain a difference, the subtractor outputting the
difference to the cue filter; and a feedback and cue controller
connected to the adaptive feedback canceller and the cue filter,
wherein the feedback and cue controller is configured to control
the cue filter to reduce a difference between an output of the ITE
microphone and a combined output that is obtained using at least
the cue filter.
Inventors: |
GRAN; Karl-Fredrik Johan;
(Malmo, SE) ; TELCS; Jacob Ulrik; (Kobenhavn N,
DK) ; MA; Guilin; (Lybgby, DK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GN ReSound A/S; |
|
|
US |
|
|
Assignee: |
GN ReSound A/S
Ballerup
DK
|
Family ID: |
51017245 |
Appl. No.: |
13/872459 |
Filed: |
April 29, 2013 |
Current U.S.
Class: |
381/313 |
Current CPC
Class: |
H04R 25/405 20130101;
H04R 25/407 20130101; H04R 2430/03 20130101 |
Class at
Publication: |
381/313 |
International
Class: |
H04R 25/00 20060101
H04R025/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2012 |
DK |
PA 2012 70836 |
Dec 28, 2012 |
EP |
12199761.3 |
Claims
1. A hearing aid comprising: a BTE hearing aid housing configured
to be worn behind a pinna of a user; at least one BTE sound input
transducer accommodated in the BTE hearing aid housing, each of
which is configured for conversion of acoustic sound into a
respective audio sound signal; an ITE microphone housing configured
to be positioned in an outer ear of the user; at least one ITE
microphone accommodated in the ITE microphone housing, each of
which is configured for conversion of acoustic sound into a
respective audio sound signal; at least one adaptive cue filter,
each of which having an input that is provided with an output from
the at least one BTE sound input transducer, wherein filter
coefficients of the at least one adaptive cue filter are adapted so
that a difference between an output of the at least one ITE
microphone and a combined output of the at least one adaptive cue
filter is reduced; a processor configured to generate a hearing
loss compensated output signal based on output by the at least one
cue filter; an output transducer for conversion of the hearing loss
compensated output signal to an auditory output signal that can be
received by a human auditory system; an adaptive feedback canceller
for feedback suppression and having an input connected to the
processor for reception of the hearing loss compensated output
signal, wherein the adaptive feedback canceller is configured to
provide at least one output modelling a feedback path between the
output transducer and the at least one BTE sound input transducer,
wherein the at least one output modelling the feedback path is
provided to a subtractor for subtraction of the at least one output
modelling the feedback path from the output of the at least one BTE
sound input transducer to obtain a difference, the subtractor
outputting the difference to the at least one adaptive cue filter;
and a feedback and cue controller connected to the adaptive
feedback canceller and the at least one adaptive cue filter,
wherein the feedback and cue controller is configured to control
the at least one adaptive cue filter so that the difference between
the output of the at least one ITE microphone and the combined
output of the at least one adaptive cue filter is reduced.
2. The hearing aid according to claim 1, wherein the filter
coefficients of the at least one adaptive cue filter are adapted
towards a solution of: min G 1 BTEC ( f , t ) G n BTEC ( f , t ) W
( f ) ( S IEC ( f , t ) - G 1 BTEC ( f , t ) S 1 BTEC ( f , t ) - -
G n ( f , t ) S n BTEC ( f , t ) p + .alpha. G 1 BTEC ( f , t ) H
FB , 1 BTEC ( f ) + + G n BTEC ( f , t ) H FB , n BTEC p
##EQU00012## wherein S.sup.IEC(f,t) is a short time spectrum at
time t of the output signal of the at least one ITE microphone, and
S.sub.1.sup.BTEC(f,t), S.sub.2.sup.BTEC(f,t), . . . ,
S.sub.n.sup.BTEC(f,t) are short time spectra at time t of the
output of the at least one BTE sound input transducer, and
G.sub.1.sup.BTEC(f,t), G.sub.2.sup.BTEC(f,t), . . . ,
G.sub.n.sup.BTEC(f,t) are transfer functions of pre-processing
filters connected to respective output(s) of the at least one BTE
sound input transducer, and H.sub.FB,1.sup.BTEC(f),
H.sub.FB,2.sup.BTEC(f), . . . , H.sub.FB,n.sup.BTEC(f) are transfer
functions of feedback path associated with the n'th BTE microphone
of the at least one BTE microphone, p is a norm factor, W(f) is a
frequency dependent weighting factor, and .alpha. is a weighting
factor balancing spatial cue accuracy and feedback performance.
3. The hearing aid according to claim 1, wherein the filter
coefficients of the at least one adaptive cue filter are adapted
towards a solution of: min G 1 BTEC ( f , t ) G n BTEC ( f , t ) W
( f ) ( S IEC ( f , t ) - G 1 BTEC ( f , t ) S 1 BTEC ( f , t ) - -
G n ( f , t ) S n BTEC ( f , t ) ) p ##EQU00013## subject to a
condition that 1 G 1 BTEC ( f , t ) H FB , 1 BTEC ( f ) + + G n
BTEC ( f , t ) H FB , n BTEC 2 .gtoreq. MSG ( f ) ##EQU00014##
wherein S.sup.IEC(f,t) is a short time spectrum at time t of the
output signal of the at least one ITE microphone, and
S.sub.1.sup.BTEC(f,t), S.sub.2.sup.BTEC(f,t), . . . ,
S.sub.n.sup.BTEC(f,t) are short time spectra at time t of the
output of the at least one BTE sound input transducer, and
G.sub.1.sup.BTEC(f,t), G.sub.2.sup.BTEC(f,t), . . . ,
G.sub.n.sup.BTEC(f,t) are transfer functions of pre-processing
filters connected to respective output(s) of the at least one BTE
sound input transducer, H.sub.FB,1.sup.BTEC(f),
H.sub.FB,2.sup.BTEC(f), . . . , H.sub.FB,n.sup.BTEC(f) are transfer
functions of feedback path associated with the n'th BTE microphone
of the at least one BTE microphone, p is a norm factor, and MSG(f)
is a maximum stable gain.
4. The hearing aid according to claim 1, wherein the filter
coefficients of the at least one adaptive cue filter comprise sets
of filter coefficients, and wherein the hearing aid further
comprises a memory for accommodation of the sets of filter
coefficients of the at least one adaptive cue filter, each of the
sets of filter coefficients is for a specific direction of arrival
with relation to the hearing aid.
5. The hearing aid according to claim 4, wherein the at least one
adaptive cue filter is loaded with the set of filter coefficients
that provides a minimum difference between the output of the at
least one ITE microphone and the combined output of the at least
one adaptive cue filter.
6. The hearing aid according to claim 5, wherein the at least one
adaptive cue filter is allowed to further adapt after the at least
one adaptive cue filter is loaded with the set of filter
coefficients that provides the minimum difference.
7. The hearing aid according to claim 1, wherein the at least one
adaptive cue filter is prevented from further adapting when changes
of values of the filter coefficients are below a prescribed
threshold.
8. The hearing aid according to claim 1, wherein the audio sound
signals from the BTE and the ITE are divided into a plurality of
frequency channels, and wherein the at least one adaptive cue
filter is configured for individually processing the audio sound
signals in one or more of the frequency channels.
9. The hearing aid according to claim 8, wherein the at least one
BTE sound input transducer is disconnected from the processor in
one or more of the frequency channels so that hearing loss
compensation is based solely on the output of the at least one ITE
microphone.
10. The hearing aid according to claim 1, wherein: the at least one
BTE sound input transducer comprises a first BTE sound input
transducer and a second BTE sound input transducer; the at least
one adaptive cue filter comprises a first adaptive cue filter and a
second adaptive cue filter; the first adaptive cue filter has an
input that is provided with an output signal from the first BTE
sound input transducer; and filter coefficients of the first
adaptive cue filter are adapted so that a difference between the
output of the at least one ITE microphone and a combined output of
the first and second adaptive cue filters is reduced.
11. The hearing aid according to claim 10, wherein: the second
adaptive cue filter has an input that is provided with an output
signal from the second BTE sound input transducer, and filter
coefficients of the second adaptive cue filter are adapted so that
a difference between the output of the at least one ITE microphone
and a combined output of the first and second adaptive cue filters
is reduced.
12. The hearing aid according to claim 2, wherein a is frequency
dependent.
13. The hearing aid according to claim 2, wherein W(f)=1.
14. The hearing aid according to claim 2, wherein p=2.
15. The hearing aid according to claim 1, wherein the filter
coefficients of the at least one adaptive cue filter are adapted so
that the difference between the output of the at least one ITE
microphone and the combined output of the at least one adaptive cue
filter is minimized.
16. The hearing aid according to claim 1, further comprising: a
sound signal transmission member for transmission of a sound signal
from a sound output in the BTE hearing aid housing at a first end
of the sound signal transmission member to the ear canal of the
user at a second end of the sound signal transmission member; and
an earpiece configured to be inserted in the ear canal of the user
for fastening and retaining the sound signal transmission member in
its intended position in the ear canal of the user.
17-23. (canceled)
Description
RELATED APPLICATION DATA
[0001] This application claims priority to, and the benefit of,
Danish Patent Application No. PA 2012 70836, filed Dec. 28, 2012,
and European Patent Application No. 12199761.3, filed Dec. 28,
2012. The disclosures of all of the above applications are
expressly incorporated by reference in their entireties herein.
FIELD
[0002] A new hearing aid is provided with improved localization of
sound sources with relation to the wearer of the hearing aid.
BACKGROUND
[0003] Hearing aid users have been reported to have poorer ability
to localize sound sources when wearing their hearing aids than
without their hearing aids. This represents a serious problem for
the mild-to-moderate hearing impaired population.
[0004] Furthermore, hearing aids typically reproduce sound in such
a way that the user perceives sound sources to be localized inside
the head. The sound is said to be internalized rather than being
externalized. A common complaint for hearing aid users when
referring to the "hearing speech in noise problem" is that it is
very hard to follow anything that is being said even though the
signal to noise ratio (SNR) should be sufficient to provide the
required speech intelligibility. A significant contributor to this
fact is that the hearing aid reproduces an internalized sound
field. This adds to the cognitive loading of the hearing aid user
and may result in listening fatigue and ultimately that the user
removes the hearing aid(s).
[0005] Thus, there is a need for a new hearing aid with improved
localization of sound sources, i.e. the new hearing aid preserves
information of the directions and distances of respective sound
sources in the sound environment with relation to the orientation
of the head of the wearer of the hearing aid.
[0006] Human beings detect and localize sound sources in
three-dimensional space by means of the human binaural sound
localization capability.
[0007] The input to the hearing consists of two signals, namely the
sound pressures at each of the eardrums, in the following termed
the binaural sound signals. Thus, if sound pressures at the
eardrums that would have been generated by a given spatial sound
field are accurately reproduced at the eardrums, the human auditory
system will not be able to distinguish the reproduced sound from
the actual sound generated by the spatial sound field itself.
[0008] It is not fully known how the human auditory system extracts
information about distance and direction to a sound source, but it
is known that the human auditory system uses a number of cues in
this determination. Among the cues are spectral cues, reverberation
cues, interaural time differences (ITD), interaural phase
differences (IPD) and interaural level differences (ILD).
[0009] The transmission of a sound wave from a sound source
positioned at a given direction and distance in relation to the
left and right ears of the listener is described in terms of two
transfer functions, one for the left ear and one for the right ear,
that include any linear distortion, such as coloration, interaural
time differences and interaural spectral differences. Such a set of
two transfer functions, one for the left ear and one for the right
ear, is called a Head-Related Transfer Function (HRTF). Each
transfer function of the HRTF is defined as the ratio between a
sound pressure p generated by a plane wave at a specific point in
or close to the appertaining ear canal (p.sub.L in the left ear
canal and p.sub.R in the right ear canal) in relation to a
reference. The reference traditionally chosen is the sound pressure
p.sub.I that would have been generated by a plane wave at a
position right in the middle of the head with the listener
absent.
[0010] The HRTF contains all information relating to the sound
transmission to the ears of the listener, including diffraction
around the head, reflections from shoulders, reflections in the ear
canal, etc., and therefore, the HRTF varies from individual to
individual.
[0011] In the following, one of the transfer functions of the HRTF
will also be termed the HRTF for convenience.
[0012] The hearing aid related transfer function is defined similar
to a HRTF, namely as the ratio between a sound pressure p generated
by the hearing aid at a specific point in the appertaining ear
canal in response to a plane wave and a reference. The reference
traditionally chosen is the sound pressure p.sub.I that would have
been generated by a plane wave at a position right in the middle of
the head with the listener absent.
[0013] The HRTF changes with direction and distance of the sound
source in relation to the ears of the listener. It is possible to
measure the HRTF for any direction and distance and simulate the
HRTF, e.g. electronically, e.g. by filters. If such filters are
inserted in the signal path between a playback unit, such as a tape
recorder, and headphones used by a listener, the listener will
achieve the perception that the sounds generated by the headphones
originate from a sound source positioned at the distance and in the
direction as defined by the transfer functions of the filters
simulating the HRTF in question, because of the true reproduction
of the sound pressures in the ears.
[0014] Binaural processing by the brain, when interpreting the
spatially encoded information, results in several positive effects,
namely better signal-to-noise ratio (SNR); direction of arrival
(DOA) estimation; depth/distance perception and synergy between the
visual and auditory systems.
[0015] The complex shape of the ear is a major contributor to the
individual spatial-spectral cues (ITD, ILD and spectral cues) of a
listener. Devices which pick up sound behind the ear will, hence,
be at a disadvantage in reproducing the HRTF since much of the
spectral detail will be lost or heavily distorted.
[0016] This is exemplified in FIGS. 1 and 2 where the angular
frequency spectrum of an open ear, i.e. non-occluded, measurement
is shown in FIG. 1 for comparison with FIG. 2 showing the
corresponding measurement on the front microphone on a behind the
ear device (BTE) using the same ear. The open ear spectrum shown in
FIG. 1 is rich in detail whereas the BTE result shown in FIG. 2 is
much more blurred and much of the spectral detail is lost.
SUMMARY
[0017] It is therefore desirable to position one or more
microphones of the hearing aid at position(s) with relation to a
user wearing the hearing aid in which spatial cues of sounds
arriving at the user is preserved. It is for example advantageous
to position a microphone in the outer ear of the user in front of
the pinna, for example at the entrance to the ear canal; or, inside
the ear canal, in order to preserve spatial cues of sounds arriving
at the ear to a much larger extent than what is possible with the
microphone behind the ear. A position below the triangular fossa
has also proven advantageous with relation to preservation of
spatial cues.
[0018] Positioning of a microphone at the entrance to the ear canal
or inside the ear canal leads to the problem that the microphone is
moved close to the sound emitting device of the hearing aid,
whereby the risk of feedback generation is increased, which in turn
limits the maximum stable gain which can be prescribed with the
hearing aid.
[0019] The standard way of solving this problem is to completely
seal off the ear canal using a custom mould. This, however,
introduces the occlusion effect as well as comfort issues with
respect to moisture and heat.
[0020] For comparison, the maximum stable gain of a BTE hearing aid
with front and rear microphones positioned behind the ear, and an
In-The-Ear (ITE) hearing aid with an open fitted microphone
positioned in the ear canal is shown in FIG. 2. It can be seen that
the ITE hearing aid has much lower maximum stable gain (MSG) than
the front and rear BTE microphones for nearly all frequencies.
[0021] In the new hearing aid, output signals of an arbitrary
configuration of microphones undergo signal processing in such a
way that spatial cues are preserved and conveyed to the user of the
hearing aid. The output signals are filtered with filters that are
configured to preserve spatial cues.
[0022] The new hearing aid provides improved localization to the
user by providing, in addition to conventionally positioned
microphones as in a BTE hearing aid, at least one ITE microphone
intended to be positioned in the outer ear of the user in front of
the pinna, e.g. at the entrance to the ear canal or immediately
below the triangular fossa; or, inside the ear canal, when in use
in order to record sound arriving at the ear of the user and
containing the desired spatial information relating to localization
of sound sources in the sound environment.
[0023] The processor of the new hearing aid combines an audio
signal of the at least one ITE microphone residing in the outer ear
of the user with the microphone signal(s) of the conventionally
positioned microphone(s) as in a BTE hearing aid in such a way that
spatial cues are preserved. An audio signal of the at least one ITE
microphone may be formed as a weighted sum of the output signals of
each microphone of the at least one ITE microphone. Other forms of
signal processing may be included in the formation of the audio
signal of the at least one ITE microphone.
[0024] Thus, a hearing aid is provided, comprising
a BTE hearing aid housing configured to be worn behind the pinna of
a user, at least one BTE sound input transducer, such as an
omni-directional microphone, a directional microphone, a transducer
for an implantable hearing aid, a telecoil, a receiver of a digital
audio datastream, etc., accommodated in the BTE hearing aid
housing, each of which is configured for conversion of sound into a
respective audio signal, an ITE microphone housing configured to be
positioned in the outer ear of the user for fastening and
retaining, in its intended position, at least one ITE microphone
accommodated in the ITE microphone housing, each of which is
configured for conversion of acoustic sound into a respective audio
signal, at least one adaptive cue filter, each of which having
[0025] an input that is provided with an output signal from a
respective one of the at least one BTE sound input transducer,
and
[0026] the filter coefficients of which are adapted so that the
difference between an output of the at least one ITE microphone and
a combined output of the at least one adaptive cue filter is
minimized, or substantially minimized, or reduced,
a processor configured to generate a hearing loss compensated
output signal based on a combination of the filtered audio signals
output by the at least one cue filter, an output transducer for
conversion of the hearing loss compensated output signal to an
auditory output signal that can be received by the human auditory
system, an adaptive feedback canceller for feedback suppression and
having
[0027] an input connected to an output of the processor for
reception of the hearing loss compensated output signal,
[0028] at least one output modelling the feedback path from the
output of the output transducer to the respective at least one BTE
microphone and connected to
[0029] a subtractor for subtraction of the at least one output from
the output of the respective at least one BTE microphone and
outputting the difference to the respective at least one adaptive
cue filter.
[0030] The hearing aid further comprises a feedback and cue
controller with inputs connected to the at least one output of the
adaptive feedback canceller and the output of the at least one
adaptive cue filter, and configured to control the at least one
adaptive cue filter so that the difference between an output of the
at least one ITE microphone and a combined output of the at least
one adaptive cue filter is reduced, preferably minimized, taking
feedback into account.
[0031] The hearing aid may further have
a sound signal transmission member for transmission of a sound
signal from a sound output in the BTE hearing aid housing at a
first end of the sound signal transmission member to the ear canal
of the user at a second end of the sound signal transmission
member, and an earpiece configured to be inserted in the ear canal
of the user for fastening and retaining the sound signal
transmission member in its intended position in the ear canal of
the user.
[0032] Throughout the present disclosure, the "output signals of
the at least one ITE microphone" may be used to identify any
analogue or digital signal forming part of the signal path from the
output of the at least one ITE microphone to an input of the
processor, including pre-processed output signals of the at least
one ITE microphone.
[0033] Likewise, the "output signals of the at least one BTE sound
input transducer" may be used to identify any analogue or digital
signal forming part of the signal path from the at least one BTE
sound input transducer to an input of the processor, including
pre-processed output signals of the at least one BTE sound input
transducer.
[0034] In use, the at least one ITE microphone is positioned so
that the output signal of the at least one ITE microphone generated
in response to the incoming sound has a transfer function that
constitutes a good approximation to the HRTFs of the user. For
example, the at least one ITE microphone may be constituted by a
single microphone positioned at the entrance to the ear canal. The
processor conveys the directional information contained in the
output signal of the at least one ITE microphone to the resulting
hearing loss compensated output signal of the processor so that the
hearing loss compensated output signal of the processor also
attains a transfer function that constitutes a good approximation
to the HRTFs of the user whereby improved localization is provided
to the user.
[0035] BTE (behind-the-ear) hearings aids are well-known in the
art. A BTE hearing aid has a BTE housing that is shaped to be worn
behind the pinna of the user. The BTE housing accommodates
components for hearing loss compensation. A sound signal
transmission member, i.e. a sound tube or an electrical conductor,
transmits a signal representing the hearing loss compensated sound
from the BTE housing into the ear canal of the user.
[0036] In order to position the sound signal transmission member
securely and comfortably at the entrance to the ear canal of the
user, an earpiece, shell, or earmould may be provided for insertion
into the ear canal of the user constituting an open solution. In an
open solution, the earpiece, shell, or earmould does not obstruct
the ear canal when it is positioned in its intended operational
position in the ear canal. Rather, there will be a passageway
through the earpiece, shell, or earmould or, between a part of the
ear canal wall and a part of the earpiece, shell, or earmould, so
that sound waves may escape from behind the earpiece, shell, or
earmould between the ear drum and the earpiece, shell, or earmould
through the passageway to the surroundings of the user. In this
way, the occlusion effect is substantially eliminated.
[0037] Typically, the earpiece, shell, or earmould is individually
custom manufactured or manufactured in a number of standard sizes
to fit the user's ear to sufficiently secure the sound signal
transmission member in its intended position in the ear canal and
prevent the earpiece from falling out of the ear, e.g., when the
user moves the jaw.
[0038] The output transducer may be a receiver positioned in the
BTE hearing aid housing. In this event, the sound signal
transmission member comprises a sound tube for propagation of
acoustic sound signals from the receiver positioned in the BTE
hearing aid housing and through the sound tube to an earpiece
positioned and retained in the ear canal of the user and having an
output port for transmission of the acoustic sound signal to the
eardrum in the ear canal.
[0039] The output transducer may be a receiver positioned in the
earpiece. In this event, the sound signal transmission member
comprises electrical conductors for propagation of audio signals
from the output of a processor in the BTE hearing aid housing
through the conductors to a receiver positioned in the earpiece for
emission of sound through an output port of the earpiece.
[0040] The ITE microphone housing accommodating at least one ITE
microphone may be combined with, or be constituted by, the earpiece
so that the at least one microphone is positioned proximate the
entrance to the ear canal when the earpiece is fastened in its
intended position in the ear canal.
[0041] The ITE microphone housing may be connected to the BTE
hearing aid housing with an arm, possibly a flexible arm that is
intended to be positioned inside the pinna, e.g. around the
circumference of the conchae abutting the antihelix and at least
partly covered by the antihelix for retaining its position inside
the outer ear of the user. The arm may be pre-formed during
manufacture, preferably into an arched shape with a curvature
slightly larger than the curvature of the antihelix, for easy
fitting of the arm into its intended position in the pinna. In one
example, the arm has a length and a shape that facilitate
positioning of the at least one ITE microphone in an operating
position immediately below the triangular fossa.
[0042] The processor may be accommodated in the BTE hearing aid
housing, or in the ear piece, or part of the processor may be
accommodated in the BTE hearing aid housing and part of the
processor may be accommodated in the ear piece. There is a one-way
or two-way communication link between circuitry of the BTE hearing
aid housing and circuitry of the earpiece. The link may be wired or
wireless.
[0043] Likewise, there is a one-way or two-way communication link
between circuitry of the BTE hearing aid housing and the at least
one ITE microphone. The link may be wired or wireless.
[0044] The processor operates to perform hearing loss compensation
while maintaining spatial information of the sound environment for
optimum spatial performance of the hearing aid and while at the
same time providing as large maximum stable gain as possible.
[0045] The output signal of the at least one ITE microphone of the
earpiece may be a combination of several pre-processed ITE
microphone signals or the output signal of a single ITE microphone
of the at least one ITE microphone. The short time spectrum for a
given time instance of the output signal of the at least one ITE
microphone of the earpiece is denoted S.sup.IEC(f,t) (IEC=In the
Ear Component).
[0046] One or more output signals of the at least one BTE sound
input transducers are provided. The spectra of these signals are
denoted S.sub.1.sup.BTEC(f,t)t), and S.sub.2.sup.BTEC(f,t), etc
(BTEC=Behind The Ear Component). The output signals may be
pre-processed. Pre-processing may include, without excluding any
form of processing; adaptive and/or static feedback suppression,
adaptive or fixed beamforming and pre-filtering.
[0047] Adaptive cue filters may be configured to adaptively filter
the audio signals of the at least one BTE sound input transducer so
that they correspond to the output signal of the at least one ITE
microphone as closely as possible. The adaptive cue filters
G.sub.1, G.sub.2, . . . , G.sub.n have the respective transfer
functions: G.sub.1(f,t), G.sub.2 (f,t), . . . , G.sub.n(f,t).
[0048] The at least one ITE microphone may operate as monitor
microphone(s) for generation of an audio signal with the desired
spatial information of the current sound environment.
[0049] Each output signal of the at least one BTE sound input
transducer is filtered with a respective adaptive cue filter, the
filter coefficients of which are adapted to provide a combined
output signal of the adaptive cue filter(s) that resembles the
audio signal provided by the at least one ITE microphone as closely
as possible.
[0050] The filter coefficients are adapted to obtain an exact or
approximate solution to the following minimization problem:
min.sub.G.sub.1.sub.(f,t) . . .
G.sub.n(f,t).parallel.S.sup.IEC(f,t)-G.sub.1(f,t)S.sub.1.sup.BTEC(f,t)-
. . . -G.sub.n(f,t)S.sub.n.sup.BTEC(f,t).parallel..sup.p (1)
wherein p is the norm. Preferably p=2.
[0051] The algorithm controlling the adaption could (without being
restricted to) e.g. be based on least mean square (LMS) or
recursive least squares (RLS), possibly normalized, optimization
methods in which p=2.
[0052] Various weights may be incorporated into the minimization
problems above so that the solution is optimized as specified by
the values of the weights. For example, frequency weights W(f) may
optimize the solution in certain one or more frequency ranges while
information in other frequency ranges may be disregarded. Thus, the
minimization problem may be modified into:
min.sub.G.sub.1.sub.(f,t) . . .
G.sub.n.sub.(f,t).parallel.W(f)((S.sup.IEC(f,t)-G.sub.1(f,t)S.sub.1.sup.B-
TEC(f,t)- . . . -G.sub.n(f,t)S.sub.n.sup.BTEC(f,t)).parallel..sup.p
(2)
[0053] Further, in one or more selected frequency ranges, only
magnitude of the transfer functions may be taken into account
during minimization while phase is disregarded, i.e. in the one or
more selected frequency range, the transfer function is substituted
by its absolute value.
[0054] Subsequent to the adaptive cue filtering, the combined
output signal of the adaptive cue filter(s) is passed on for
further hearing loss compensation processing, e.g. with a
compressor.
[0055] In this way, only signals from the at least one BTE sound
input transducer is possibly amplified as a result of hearing loss
compensation while the audio signal of the alt least one ITE
microphone is not included in the hearing loss compensation
processing, whereby possible feedback from the output transducer to
the at least one ITE microphone is reduced, preferably minimized,
and a large maximum stable gain can be provided.
[0056] For example, in a hearing aid with one ITE microphone, and
two BTE microphones constituting the at least one BTE sound input
transducer, and in the event that the incident sound field consist
of sound emitted by a single speaker, the emitted sound having the
short time spectrum X(f,t); then, under the assumption that no
pre-processing is performed with relation to the ITE microphone
signal and that the ITE microphone reproduces the actual HRTF
perfectly then the following signals are provided:
S.sup.IEC(f,t)=HRTF(f)X(f,t) (3)
S.sub.1,2.sup.BTEC(f,t)=H.sub.1,2(f)X(f,t) (4)
where H.sub.1,2(f) are the hearing aid related transfer functions
of the two BTE microphones.
[0057] After sufficient adaptation, the hearing aid impulse
response convolved with the resulting adapted filters and summed
will be equal the actual HRTF so that
lim.sub.t.fwdarw..infin.G.sub.1(f,t)H.sub.1(f)+G.sub.2(f,t)H.sub.2(f)=HR-
TF(f) (5)
[0058] If the speaker moves and thereby changes the HRTF, the
adaptive cue filters, i.e. the algorithm adjusting the filter
coefficients, adapt towards the new minimum of minimization problem
(2). The time constants of the adaptation are set to appropriately
respond to changes of the current sound environment.
[0059] Feedback may be taken into account by performing the
solution of the minimization problem (2) subject to the condition
that the gain of the feedback loops must be less than one, i.e.
subject to the condition that
1 G 1 BTEC ( f , t ) H FB , 1 BTEC ( f ) + + G n BTEC ( f , t ) H
FB , n BTEC 2 .gtoreq. MSG ( f ) ( 6 ) ##EQU00001##
wherein H.sub.FB,1.sup.BTEC(f), H.sub.FB,2.sup.BTEC(f), . . . ,
H.sub.FB,n.sup.BTEC(f) are the transfer functions of the feedback
path associated with the n'th BTE microphone of the at least one
BTE microphone, and MSG(f) is the maximum stable gain, In this way,
it is ensured that a desired maximum stable gain will be
available.
[0060] Alternatively, the requirement of spatial cue preservation
and feedback cancellation may be balanced by solving:
min G 1 BTEC ( f , t ) G n BTEC ( f , t ) S IEC ( f , t ) - G 1
BTEC ( f , t ) S 1 BTEC ( f , t ) - - G n ( f , t ) S n BTEC ( f ,
t ) p + .alpha. G 1 BTEC ( f , t ) H FB , 1 BTEC ( f ) + + G n BTEC
( f , t ) H FB , n BTEC p ( 7 ) ##EQU00002##
wherein p is the norm factor, e.g. p=2, and .alpha. is a weighting
factor balancing spatial cue accuracy and feedback performance.
.alpha. may be frequency dependent so that in a frequency range
with low probability of feedback, .alpha. may be of low value, and
in a frequency range with high probability of feedback, .alpha. may
be of high value in order to take feedback appropriately into
account in the frequency range in question.
[0061] The transfer functions H.sub.FB,1.sup.BTEC(f),
H.sub.FB,2.sup.BTEC(f), . . . , H.sub.FB,n.sup.BTEC(f) of the
feedback paths may be modelled or approximated by an adaptive
feedback cancellation circuit well-known in the art.
[0062] Various weights may be incorporated into the minimization
problems above so that the solution is optimized as specified by
the values of the weights. For example, frequency weights W(f) may
optimize the solution in certain one or more frequency ranges.
Thus, the minimization problem may be modified into:
Min G 1 BTEC ( f , t ) G n BTEC ( f , t ) W ( f ) ( S IEC ( f , t )
- G 1 BTEC ( f , t ) S 1 BTEC ( f , t ) - - G n ( f , t ) S n BTEC
( f , t ) ) p ( 8 ) ##EQU00003##
subject to the condition that
1 G 1 BTEC ( f , t ) H FB , 1 BTEC ( f ) + + G n BTEC ( f , t ) H
FB , n BTEC 2 .gtoreq. MSG ( f ) or ( 9 ) min G 1 BTEC ( f , t ) G
n BTEC ( f , t ) W ( f ) ( S IEC ( f , t ) - G 1 BTEC ( f , t ) S 1
BTEC ( f , t ) - - G n BTEC ( f , t ) S n BTEC ( f , t ) ) p +
.alpha. G 1 BTEC ( f , t ) H FB , 1 BTEC ( f ) + + G n BTEC ( f , t
) H FB , n BTEC P ( 10 ) ##EQU00004##
[0063] The target transfer function need not be defined by the HRTF
for the various directions I. Any transfer function that includes
spatial cues may be used as the target transfer function.
[0064] As used herein, the terms "processor", "signal processor",
"controller", "system", etc., are intended to refer to CPU-related
entities, either hardware, a combination of hardware and software,
software, or software in execution.
[0065] For example, a "processor", "signal processor",
"controller", "system", etc., may be, but is not limited to being,
a process running on a processor, a processor, an object, an
executable file, a thread of execution, and/or a program.
[0066] By way of illustration, the terms "processor", "signal
processor", "controller", "system", etc., designate both an
application running on a processor and a hardware processor. One or
more "processors", "signal processors", "controllers", "systems"
and the like, or any combination hereof, may reside within a
process and/or thread of execution, and one or more "processors",
"signal processors", "controllers", "systems", etc., or any
combination hereof, may be localized on one hardware processor,
possibly in combination with other hardware circuitry, and/or
distributed between two or more hardware processors, possibly in
combination with other hardware circuitry.
[0067] The hearing aid may be a multi-channel hearing aid in which
signals to be processed are divided into a plurality of frequency
channels, and wherein signals are processed individually in each of
the frequency channels. The adaptive feedback cancellation
circuitry may also be divided into the plurality of frequency
channels; or, the adaptive feedback cancellation circuitry may
still operate in the entire frequency range; or, may be divided
into other frequency channels, typically fewer frequency channels,
than the other circuitry is divided into.
[0068] The processor may be configured for processing the output
signals of the at least one ITE microphone and the at least one BTE
sound input transducer in such a way that the hearing loss
compensated output signal substantially preserves spatial cues in a
selected frequency band.
[0069] The selected frequency band may comprise one or more of the
frequency channels, or all of the frequency channels. The selected
frequency band may be fragmented, i.e. the selected frequency band
need not comprise consecutive frequency channels.
[0070] The plurality of frequency channels may include warped
frequency channels, for example all of the frequency channels may
be warped frequency channels.
[0071] Outside the selected frequency band, the at least one ITE
microphone may be connected conventionally as an input source to
the processor of the hearing aid and may cooperate with the
processor of the hearing aid in a well-known way.
[0072] In this way, the at least one ITE microphone supplies the
input to the hearing aid at frequencies where the hearing aid is
capable of supplying the desired gain with this configuration. In
the selected frequency band, wherein the hearing aid cannot supply
the desired gain with this configuration, the microphones of BTE
hearing aid housing are included in the signal processing as
disclosed above. In this way, the gain can be increased while
simultaneously maintain the spatial information about the sound
environment provided by the at least one ITE microphone.
[0073] The hearing aid may for example comprise a first filter
connected between the processor input and the at least one ITE
microphone, and a second complementary filter connected between the
processor input and a combined output of the at least one BTE sound
input transducer, the filters passing and blocking frequencies in
complementary frequency bands so that one of the at least one ITE
microphone and the combined output of at least one BTE sound input
transducer constitutes the main part of the input signal supplied
to the processor input in one frequency band, and the other one of
the at least one ITE microphone and the combined output of at least
one BTE sound input transducer constitutes the main part of the
input signal supplied to the processor input in the complementary
frequency band.
[0074] In this way, the at least one ITE microphone may be used as
the sole input source to the processor in a frequency band wherein
the required gain for hearing loss compensation can be applied to
the output signal of the at least one ITE microphone. Outside this
frequency band, the combined output signal of the at least one BTE
sound input transducer is applied to the processor for provision of
the required gain.
[0075] The combination of the signals could e.g. be based on
different types of band pass filtering.
[0076] A hearing aid includes: a BTE hearing aid housing configured
to be worn behind a pinna of a user; at least one BTE sound input
transducer accommodated in the BTE hearing aid housing, each of
which is configured for conversion of acoustic sound into a
respective audio sound signal; an ITE microphone housing configured
to be positioned in an outer ear of the user; at least one ITE
microphone accommodated in the ITE microphone housing, each of
which is configured for conversion of acoustic sound into a
respective audio sound signal; at least one adaptive cue filter,
each of which having an input that is provided with an output from
the at least one BTE sound input transducer, wherein filter
coefficients of the at least one adaptive cue filter are adapted so
that a difference between an output of the at least one ITE
microphone and a combined output of the at least one adaptive cue
filter is reduced; a processor configured to generate a hearing
loss compensated output signal based on output by the at least one
cue filter; an output transducer for conversion of the hearing loss
compensated output signal to an auditory output signal that can be
received by a human auditory system; an adaptive feedback canceller
for feedback suppression and having an input connected to the
processor for reception of the hearing loss compensated output
signal, wherein the adaptive feedback canceller is configured to
provide at least one output modelling a feedback path between the
output transducer and the at least one BTE sound input transducer,
wherein the at least one output modelling the feedback path is
provided to a subtractor for subtraction of the at least one output
modelling the feedback path from the output of the at least one BTE
sound input transducer to obtain a difference, the subtractor
outputting the difference to the at least one adaptive cue filter;
and a feedback and cue controller connected to the adaptive
feedback canceller and the at least one adaptive cue filter,
wherein the feedback and cue controller is configured to control
the at least one adaptive cue filter so that the difference between
the output of the at least one ITE microphone and the combined
output of the at least one adaptive cue filter is reduced.
[0077] Optionally, the filter coefficients of the at least one
adaptive cue filter may be adapted towards a solution of:
min G 1 BTEC ( f , t ) G n BTEC ( f , t ) W ( f ) ( S IEC ( f , t )
- G 1 BTEC ( f , t ) S 1 BTEC ( f , t ) - - G n ( f , t ) S n BTEC
( f , t ) p + .alpha. G 1 BTEC ( f , t ) H FB , 1 BTEC ( f ) + + G
n BTEC ( f , t ) H FB , n BTEC p ##EQU00005##
wherein S.sup.IEc(f,t) is a short time spectrum at time t of the
output signal of the at least one ITE microphone, and
S.sub.1.sup.BTEC(f,t)t), S.sub.2.sup.BTEC(f,t), . . . ,
S.sub.n.sup.BTEC(f,t) are short time spectra at time t of the
output of the at least one BTE sound input transducer, and
G.sub.1.sup.BTEC(f,t), G.sub.2.sup.BTEC(f,t), . . . ,
G.sub.n.sup.BTEC(f,t) are transfer functions of pre-processing
filters connected to respective output(s) of the at least one BTE
sound input transducer, and H.sub.FB,1.sup.BTEC(f),
H.sub.FB,2.sup.BTEC(f), . . . , H.sub.FB,n.sup.BTEC(f) are transfer
functions of feedback path associated with the n'th BTE microphone
of the at least one BTE microphone, p is a norm factor, W(f) is a
frequency dependent weighting factor, and .alpha. is a weighting
factor balancing spatial cue accuracy and feedback performance.
[0078] Optionally, the filter coefficients of the at least one
adaptive cue filter may be adapted towards a solution of:
min.sub.G.sub.1.sub.BTEC.sub.(f,t) . . .
G.sub.n.sub.BTEC.sub.(f,t).parallel.W(f)(S.sup.IEC(f,t)-G.sub.1.sup.BTEC(-
f,t)S.sub.1.sup.BTEC(f,t)- . . .
-G.sub.n(f,t)S.sub.n.sup.BTEC(f,t)).parallel..sup.p subject to a
condition that
1 G 1 BTEC ( f , t ) H FB , 1 BTEC ( f ) + + G n BTEC ( f , t ) H
FB , n BTEC 2 .gtoreq. MSG ( f ) ##EQU00006##
Wherein S.sup.IEC(f,t) is a short time spectrum at time t of the
output signal of the at least one ITE microphone, and
S.sub.1.sup.BTEC(f,t), S.sub.2.sup.BTEC(f,t), . . . ,
S.sub.n.sup.BTEC(f,t) are short time spectra at time t of the
output of the at least one BTE sound input transducer, and
G.sub.1.sup.BTEC(f,t), G.sub.2.sup.BTEC(f,t), . . . ,
G.sub.n.sup.BTEC(f,t) are transfer functions of pre-processing
filters connected to respective output(s) of the at least one BTE
sound input transducer, H.sub.FB,1.sup.BTEC(f),
H.sub.FB,2.sup.BTEC(f), . . . , H.sub.FB,n.sup.BTEC(f) are transfer
functions of feedback path associated with the n'th BTE microphone
of the at least one BTE microphone, p is a norm factor, and MSG(f)
is a maximum stable gain.
[0079] Optionally, the filter coefficients of the at least one
adaptive cue filter may comprise sets of filter coefficients, and
wherein the hearing aid further comprises a memory for
accommodation of the sets of filter coefficients of the at least
one adaptive cue filter, each of the sets of filter coefficients is
for a specific direction of arrival with relation to the hearing
aid.
[0080] Optionally, the at least one adaptive cue filter may be
loaded with the set of filter coefficients that provides a minimum
difference between the output of the at least one ITE microphone
and the combined output of the at least one adaptive cue
filter.
[0081] Optionally, the at least one adaptive cue filter may be
allowed to further adapt after the at least one adaptive cue filter
is loaded with the set of filter coefficients that provides the
minimum difference.
[0082] Optionally, the at least one adaptive cue filter may be
prevented from further adapting when changes of values of the
filter coefficients are below a prescribed threshold.
[0083] Optionally, the audio sound signals from the BTE and the ITE
may be divided into a plurality of frequency channels, and wherein
the at least one adaptive cue filter may be configured for
individually processing the audio sound signals in one or more of
the frequency channels
[0084] Optionally, the at least one BTE sound input transducer may
be disconnected from the processor in one or more of the frequency
channels so that hearing loss compensation is based solely on the
output of the at least one ITE microphone.
[0085] Optionally, the at least one BTE sound input transducer may
comprise a first BTE sound input transducer and a second BTE sound
input transducer, and the at least one adaptive cue filter may
comprise a first adaptive cue filter and a second adaptive cue
filter; the first adaptive cue filter may have an input that is
provided with an output signal from the first BTE sound input
transducer; and filter coefficients of the first adaptive cue
filter may be adapted so that a difference between the output of
the at least one ITE microphone and a combined output of the first
and second adaptive cue filters is reduced.
[0086] Optionally, the second adaptive cue filter may have an input
that is provided with an output signal from the second BTE sound
input transducer, and filter coefficients of the second adaptive
cue filter may be adapted so that a difference between the output
of the at least one ITE microphone and a combined output of the
first and second adaptive cue filters is reduced.
[0087] Optionally, .alpha. may be frequency dependent.
[0088] Optionally, W(f) may be equal to 1.
[0089] Optionally, p may be equal to 2.
[0090] Optionally, the filter coefficients of the at least one
adaptive cue filter may be adapted so that the difference between
the output of the at least one ITE microphone and the combined
output of the at least one adaptive cue filter is minimized.
[0091] Optionally, the hearing aid may further include: a sound
signal transmission member for transmission of a sound signal from
a sound output in the BTE hearing aid housing at a first end of the
sound signal transmission member to the ear canal of the user at a
second end of the sound signal transmission member; and an earpiece
configured to be inserted in the ear canal of the user for
fastening and retaining the sound signal transmission member in its
intended position in the ear canal of the user.
[0092] A hearing aid includes: a BTE hearing aid housing; a BTE
sound input transducer accommodated in the BTE hearing aid housing;
an ITE microphone housing; an ITE microphone accommodated in the
ITE microphone housing; a cue filter having an input that is
provided with an output from the BTE sound input transducer; a
processor configured to generate a hearing loss compensated output
signal based on an output by the cue filter; an output transducer
for conversion of the hearing loss compensated output signal to an
auditory output signal; an adaptive feedback canceller configured
to provide an output modelling a feedback path between the output
transducer and the BTE sound input transducer, wherein the output
modelling the feedback path is provided to a subtractor for
subtraction of the output modelling the feedback path from the
output of the BTE sound input transducer to obtain a difference,
the subtractor outputting the difference to the cue filter; and a
feedback and cue controller connected to the adaptive feedback
canceller and the cue filter, wherein the feedback and cue
controller is configured to control the cue filter to reduce a
difference between an output of the ITE microphone and a combined
output that is obtained using at least the cue filter.
[0093] Optionally, the combined output may be obtained using the
output from the cue filter and another output from another cue
filter.
[0094] Optionally, the feedback and cue controller may be
configured to control the cue filter to minimize the difference
between the output of the ITE microphone and the combined
output.
[0095] Optionally, the cue filter may comprise sets of filter
coefficients, and wherein the hearing aid may further comprise a
memory for accommodation of the sets of filter coefficients, each
of the sets of filter coefficients is for a specific direction of
arrival with relation to the hearing aid.
[0096] Optionally, the cue filter may be loaded with the set of
filter coefficients that provides a minimum difference between the
output of the ITE microphone and the combined output.
[0097] Optionally, the cue filter may be allowed to further adapt
after the cue filter is loaded with the set of filter coefficients
that provides the minimum difference.
[0098] Optionally, the cue filter may be prevented from further
adapting when a change of filter coefficient value is below a
prescribed threshold.
[0099] Other and further aspects and features will be evident from
reading the following detailed description of the embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0100] The drawings illustrate the design and utility of
embodiments, in which similar elements are referred to by common
reference numerals. These drawings are not necessarily drawn to
scale. In order to better appreciate how the above-recited and
other advantages and objects are obtained, a more particular
description of the embodiments will be rendered, which are
illustrated in the accompanying drawings. These drawings depict
only exemplary embodiments and are not therefore to be considered
limiting in the scope of the claims.
[0101] FIG. 1 shows a plot of the angular frequency spectrum of an
open ear,
[0102] FIG. 2 shows a plot of the angular frequency spectrum of a
BTE front microphone worn at the same ear,
[0103] FIG. 3 shows plots of maximum stable gain of a BTE front and
rear microphones and an open fitted ITE microphone positioned in
the ear canal,
[0104] FIG. 4 schematically illustrates an exemplary new hearing
aid,
[0105] FIG. 5 schematically illustrates another exemplary new
hearing aid,
[0106] FIG. 6 shows in perspective a new hearing aid with an
ITE-microphone in the outer ear of a user,
[0107] FIG. 7 shows a schematic block diagram of a new hearing aid
with adaptive cue filters,
[0108] FIG. 8 shows a schematic block diagram of the hearing aid of
FIG. 7 with added feedback cancellation,
[0109] FIG. 9 shows a schematic block diagram of a new hearing aid
with an arbitrary number of microphones,
[0110] FIG. 10 shows a schematic block diagram of a new hearing
aid,
[0111] FIG. 11 shows a schematic block diagram of the hearing aid
of FIG. 10 with added feedback cancellation, and
[0112] FIG. 12 shows a schematic block diagram of the hearing aid
of FIG. 11 with added adaptive filtering.
DETAILED DESCRIPTION
[0113] Various embodiments are described hereinafter with reference
to the figures. It should be noted that the figures are not
necessarily drawn to scale and that elements of similar structures
or functions are represented by like reference numerals throughout
the figures. It should also be noted that the figures are only
intended to facilitate the description of the embodiments. They are
not intended as an exhaustive description of the claimed invention
or as a limitation on the scope of the claimed invention. In
addition, an illustrated embodiment needs not have all the aspects
or advantages shown. An aspect or an advantage described in
conjunction with a particular embodiment is not necessarily limited
to that embodiment and can be practiced in any other embodiments
even if not so illustrated, or if not so explicitly described.
[0114] FIG. 4 schematically illustrates a BTE hearing aid 10
comprising a BTE hearing aid housing 12 (not shown--outer walls
have been removed to make internal parts visible) to be worn behind
the pinna 100 of a user. The BTE housing 12 accommodates at least
one BTE sound input transducer 14, 16 with a front microphone 14
and a rear microphone 16 for conversion of a sound signal into a
microphone audio signal, optional pre-filters (not shown) for
filtering the respective microphone audio signals, A/D converters
(not shown) for conversion of the respective microphone audio
signals into respective digital microphone audio signals that are
input to a processor 18 configured to generate a hearing loss
compensated output signal based on the input digital audio
signals.
[0115] The hearing loss compensated output signal is transmitted
through electrical wires contained in a sound signal transmission
member 20 to a receiver 22 for conversion of the hearing loss
compensated output signal to an acoustic output signal for
transmission towards the eardrum of a user and contained in an
earpiece 24 that is shaped (not shown) to be comfortably positioned
in the ear canal of a user for fastening and retaining the sound
signal transmission member in its intended position in the ear
canal of the user as is well-known in the art of BTE hearing
aids.
[0116] The earpiece 24 also holds one ITE microphone 26 that is
positioned at the entrance to the ear canal when the earpiece is
positioned in its intended position in the ear canal of the user.
The ITE microphone 26 is connected to an A/D converter (not shown)
and optional to a pre-filter (not shown) in the BTE housing 12,
with electrical wires (not visible) contained in the sound
transmission member 20.
[0117] The BTE hearing aid 10 is powered by battery 28.
[0118] Various possible functions of the processor 18 are disclosed
above and some of these in more detail below.
[0119] FIG. 5 schematically illustrates another BTE hearing aid 10
similar to the hearing aid shown in FIG. 1, except for the
difference that in FIG. 5, the receiver 22 is positioned in the
hearing aid housing 12 and not in the earpiece 24, so that acoustic
sound output by the receiver 22 is transmitted through the sound
tube 20 and towards the eardrum of the user when the earpiece 24 is
positioned in its intended position in the ear canal of the
user.
[0120] The positioning of the ITE microphone 26 proximate the
entrance to the ear canal of the user when the BTE hearing aids 10
of FIGS. 4 and 5 are used is believed to lead to a good
reproduction of the HRTFs of the user.
[0121] FIG. 6 shows a BTE hearing aid 10 in its operating position
with the BTE housing 12 behind the ear, i.e. behind the pinna 100,
of the user. The illustrated BTE hearing aid 10 is similar to the
hearing aids shown in FIGS. 4 and 5 except for the fact that the
ITE microphone 26 is positioned in the outer ear of the user
outside the ear canal at the free end of an arm 30. The arm 30 is
flexible and the arm 30 is intended to be positioned inside the
pinna 100, e.g. around the circumference of the conchae 102 behind
the tragus 104 and antitragus 106 and abutting the antihelix 108
and at least partly covered by the antihelix for retaining its
position inside the outer ear of the user. The arm may be
pre-formed during manufacture, preferably into an arched shape with
a curvature slightly larger than the curvature of the antihelix
104, for easy fitting of the arm 30 into its intended position in
the pinna. The arm 30 contains electrical wires (not visible) for
interconnection of the ITE microphone 26 with other parts of the
BTE hearing aid circuitry.
[0122] In one example, the arm 30 has a length and a shape that
facilitate positioning of the ITE microphone 26 in an operating
position below the triangular fossa.
[0123] FIG. 7 is a block diagram illustrating one example of signal
processing in the new hearing aid 10. The illustrated hearing aid
10 has a front microphone 14 and a rear microphone 16 accommodated
in the BTE hearing aid housing configured to be worn behind the
pinna of the user, for conversion of sound signals arriving at the
microphones 14, 16 into respective audio signals 33, 35. Further,
the illustrated hearing aid 10 has an ITE microphone 26
accommodated in an earpiece (not shown) to be positioned in the
outer ear of the user, for conversion of sound signals arriving at
the microphone 26 into audio signal 31.
[0124] The microphone audio signals 31, 33, 35 are digitized and
pre-processed, such as pre-filtered, in respective pre-processors
32, 34, 36. The pre-processed audio signals 38, 40 of the front and
rear microphones 14, 16 are filtered in respective adaptive cue
filters 42, 44, and the adaptively filtered signals 46, 48 are
added to each other in adder 50 and the combined signal 52 is input
to processor 18 for hearing loss compensation. The hearing loss
compensated signal 54 is output to the receiver 22 that converts
the signal 54 to an acoustic output signal for transmission towards
the ear drum of the user.
[0125] Adaptation of the filter coefficients of adaptive cue
filters 42, 44 are controlled by adaptive controller 56 that
controls the adaptation of the filter coefficients to reduce, and
preferably eventually minimize, the difference 58 between the
output 52 of adder 46 and the pre-processed ITE microphone audio
signal 60, output by subtractor 62. In this way, the input signal
52 to the processor 18 models the microphone audio signal 60 of the
ITE microphone 26, and thus also substantially models the HRTFs of
the user.
[0126] The pre-processed output signal 60 of the ITE microphone 26
of the earpiece has a short time spectrum denoted S.sup.IEC(f,t)
(IEC=In the Ear Component).
[0127] The spectra of the pre-processed audio signals 38, 40 of the
front and rear microphones 14, 16 are denoted
S.sub.1.sup.BTEC(f,t), and S.sub.2.sup.BTEC(f,t) (BTEC=Behind The
Ear Component).
[0128] Pre-processing may include, without excluding any form of
processing; adaptive and/or static feedback suppression, adaptive
or fixed beamforming and pre-filtering.
[0129] The adaptive controller 56 is configured to control the
filter coefficients of adaptive cue filters 42, 44 so that their
summed output 52 corresponds to the pre-processed output signal 60
of the ITE microphone 26 as closely as possible.
[0130] The adaptive cue filters 42, 44 have the respective transfer
functions: G.sub.1(f,t), and G.sub.2(f,t)
[0131] The ITE microphone 26 operates as monitor microphone for
generation of an audio signal 60 with the desired spatial
information of the current sound environment due to its positioning
in the outer ear of the user.
[0132] Thus, the filter coefficients of the adaptive cue filters
34, 36 are adapted to obtain an exact or approximate solution to
the minimization problem:
min.sub.G.sub.1.sub.(f,t),G.sub.2.sub.(f,t).parallel.S.sup.IEC(f,t)-G.su-
b.1(f,t)S.sub.1.sup.BTEC(f,t)-G.sub.2(f,t)S.sub.n.sup.BTEC(f,t).parallel..-
sup.p (11)
wherein p is the norm-factor, preferably p=2.
[0133] The algorithm controlling the adaption could (without being
restricted to) e.g. be based on least mean square (LMS) or
recursive least squares (RLS), possibly normalized, optimization
methods in which p=2.
[0134] Subsequent to the adaptive cue filtering, the combined
output signal 52 of the adaptive cue filters 42, 44 is passed on
for further hearing loss compensation processing, e.g. in a
compressor. In this way, only signals from the front and rear
microphones 14, 16 are possibly amplified as a result of hearing
loss compensation while the audio signal 60 of the ITE microphone
26 is not processed in the processor 18 configured for hearing loss
processing, whereby possible feedback from the output transducer 22
to the ITE microphone 26 is reduced, preferably minimized, and a
large maximum stable gain can be provided.
[0135] For example, in the event that the incident sound field
consists of sound emitted by a single speaker, the emitted sound
having the short time spectrum X(f,t); then, under the assumption
that no pre-processing is performed with relation to the ITE
microphone signal 60 and that the ITE microphone 26 reproduces the
actual HRTF perfectly then the following signals are provided:
S.sup.IEC(f,t)=HRTF(f)X(f,t) (12)
S.sub.1,2.sup.BTEC(f,t)=H.sub.1,2(f)X(f,t) (13)
where H.sub.1,2(f) are the hearing aid related transfer functions
of the two BTE microphones 14, 16.
[0136] After sufficient adaptation, the hearing aid impulse
response convolved with the resulting adapted filters and summed
will be equal the actual HRTF so that
lim.sub.t.fwdarw..infin.G.sub.1(f,t)H.sub.1(f)+G.sub.2(f,t)H.sub.2(f)=HR-
TF(f) (14)
[0137] If the speaker moves and thereby changes the actual HRTF,
the adaptive cue filters 42, 44, i.e. the adaptive controller 56 by
adjusting the filter coefficients, adapt towards the new minimum of
the minimization problem (11). The time constants of the adaptation
are set to appropriately respond to changes of the current sound
environment.
[0138] In the event that feedback occurs in the hearing aid,
adaptation may be stopped, i.e. the filter coefficients may be
prevented from changing, or the adaptation rate may be slowed down,
in order to avoid that feedback is transferred from the audio
signal of the at least one ITE microphone to the output signal(s)
of the at least one BTE sound input transducer during presence of
feedback.
[0139] The filter coefficients of the adaptive cue filters 42, 44
may be predetermined so that a set of filter coefficients is
provided for a specific HRTF.
[0140] The sets of filter coefficients, one set for each
predetermined HRTF, may be determined using a manikin, such as
KEMAR. The filter coefficients are determined for at number of
direction of arrivals for the hearing aid as disclosed above;
however under controlled conditions and allowing adaptation of long
duration. In this way, an approximation to the individual HRTFs is
provided that can be of sufficient accuracy for the hearing aid
user to maintain sense of direction when wearing the hearing
aid.
[0141] During use, the set of filter coefficients is selected that
reduces, and preferably eventually minimizes, the difference
between the combined output signal, possibly pre-processed, of the
at least one BTE sound input transducer and the output signal,
possibly pre-processed, of the at least one ITE microphone. During
use, the adaptive cue filter may be allowed to further adapt to the
individual HRTF of the user in question. The adaptation may be
stopped when the filter coefficients have become stable so that the
at least one ITE microphone is no longer used for the HRTF in
question.
[0142] The new hearing aid circuitry shown in FIG. 7 may operate in
the entire frequency range of the hearing aid 10.
[0143] The hearing aid 10 shown in FIG. 7 may be a multi-channel
hearing aid in which microphone audio signals 38, 40, 60 to be
processed are divided into a plurality of frequency channels, and
wherein signals are processed individually in each of the frequency
channels.
[0144] For a multi-channel hearing aid 10, FIG. 7 may illustrate
the circuitry and signal processing in a single frequency channel.
The circuitry and signal processing may be duplicated in a
plurality of the frequency channels, e.g. in all of the frequency
channels.
[0145] For example, the signal processing illustrated in FIG. 7 may
be performed in a selected frequency band, e.g. selected during
fitting of the hearing aid to a specific user at a dispenser's
office.
[0146] The selected frequency band may comprise one or more of the
frequency channels, or all of the frequency channels. The selected
frequency band may be fragmented, i.e. the selected frequency band
need not comprise consecutive frequency channels.
[0147] The plurality of frequency channels may include warped
frequency channels, for example all of the frequency channels may
be warped frequency channels.
[0148] Outside the selected frequency band, the ITE microphone 26
may be connected conventionally as an input source to the processor
18 of the hearing aid 10 and may cooperate with the processor 18 of
the hearing aid 10 in a well-known way.
[0149] In this way, the ITE microphone supplies the input to the
hearing aid at frequencies where the hearing aid is capable of
supplying the desired gain with this configuration. In the selected
frequency band, wherein the hearing aid cannot supply the desired
gain with this configuration, the microphones 14, 16 of BTE hearing
aid housing are included in the signal processing as disclosed
above. In this way, the gain can be increased while the spatial
information of the sound environment as provided by the ITE
microphone is simultaneously maintained.
[0150] FIG. 8 is a block diagram illustrating a new hearing aid 10
similar to the hearing aid 10 shown in FIG. 7 except for the fact
that adaptive feedback cancellation circuitry has been added,
including an adaptive feedback filter 70 with an input 72 connected
to the output of the hearing aid processor 18 and with outputs
74-1, 76-1, 76-2, each of which is connected to a respective
subtractor 78-1, 80-1, 80-2 for subtraction of each output 74-1,
76-1, 76-2 from a respective microphone output 31, 33, 35 to
provide a respective feedback compensated signal 82-1, 84-1, 84-2
as is well-known in the art. Each feedback compensated signal 82-1,
84-1, 84-2 is fed to the corresponding pre-processor 32, 34, 36,
and also to the adaptive feedback filter 70 for control of the
adaption of the adaptive feedback filter 70. The adaptive feedback
filter outputs 74-1, 76-1, 76-2 provide signals that constitute
approximations of corresponding feedback signals travelling from
the output transducer 22 to the respective microphone 14, 16, 26 as
is well-known in the art. The outputs 76-1, 76-2 approximating
feedback signals of the BTE microphones are further connected to
the adaptive controller 56.
[0151] The adaptive controller 56 of FIG. 8 controls adjustment of
the filter coefficients of adaptive cue filters 38, 40 by solving
minimization problem (11) subject to the condition that
1 G 1 ( f , t ) H FB , 1 BTEC ( f ) + G 2 ( f , t ) H FB , n BTEC 2
.gtoreq. MSG ( f ) ( 15 ) ##EQU00007##
or by solving minimization problem
min G 1 ( f , t ) G 2 ( f , t ) W ( f ) ( S IEC ( f , t ) - G 1 ( f
, t ) S 1 BTEC ( f , t ) - G 2 ( f , t ) S 2 BTEC ( f , t ) ) p +
.alpha. G 1 ( f , t ) H FB , 1 BTEC ( f ) + + G 2 ( f , t ) H FB ,
2 BTEC p ( 16 ) ##EQU00008##
in order to preserve spatial cue and simultaneously take feedback
into account.
[0152] Typically p=2, and/or W(f)=1.
[0153] The new hearing aid circuitry shown in FIG. 8 may operate in
the entire frequency range of the hearing aid 10.
[0154] The hearing aid 10 shown in FIG. 8 may be a multi-channel
hearing aid in which microphone audio signals 38, 40, 60 to be
processed are divided into a plurality of frequency channels, and
wherein signals are processed individually in each of the frequency
channels possibly apart from the adaptive feedback cancellation
circuitry 70, 72, 74-1, 74-2, 76-1, 76-2, 78-1, 78-2, 80-1, 80-2,
82-1, 82-2, 84-1, 84-2 that may still operate in the entire
frequency range; or, may be divided into other frequency channels,
typically fewer frequency channels than the remaining illustrated
circuitry.
[0155] For a multi-channel hearing aid 10, the part of FIG. 8
corresponding to the circuitry of FIG. 7 may illustrate the
circuitry and signal processing in a single frequency channel,
while the adaptive circuitry that may still operate in the entire
frequency range; or, may be divided into other frequency channels,
typically fewer frequency channels than the remaining illustrated
circuitry.
[0156] The circuitry and signal processing may be duplicated in a
plurality of the frequency channels, e.g. in all of the frequency
channels.
[0157] For example, the signal processing illustrated in FIG. 8 may
be performed in a selected frequency band, e.g. selected during
fitting of the hearing aid to a specific user at a dispenser's
office.
[0158] The selected frequency band may comprise one or more of the
frequency channels, or all of the frequency channels. The selected
frequency band may be fragmented, i.e. the selected frequency band
need not comprise consecutive frequency channels.
[0159] The plurality of frequency channels may include warped
frequency channels, for example all of the frequency channels may
be warped frequency channels.
[0160] Outside the selected frequency band, the at least one ITE
microphone may be connected conventionally as an input source to
the processor of the hearing aid and may cooperate with the
processor of the hearing aid in a well-known way.
[0161] In this way, the at least one ITE microphone supplies the
input to the hearing aid at frequencies where the hearing aid is
capable of supplying the desired gain with this configuration. In
the selected frequency band, wherein the hearing aid cannot supply
the desired gain with this configuration, the microphones of BTE
hearing aid housing are included in the signal processing as
disclosed above. In this way, the gain can be increased while
simultaneously maintain the spatial information about the sound
environment provided by the at least one ITE microphone.
[0162] FIG. 9 is a block diagram illustrating a new hearing aid 10
similar to the hearing aid 10 shown in FIG. 7 and operating in a
way similar to the hearing aid 10 shown in FIG. 7, except for the
fact that the circuit has been generalized to include an arbitrary
number N of ITE microphones 26-1, 26-2, . . . , 26-N, and an
arbitrary number M of BTE microphones 14-1, 14-2, . . . , 14-M. In
FIG. 7, N=1 and M=2. In FIG. 9, N and M can be any non-negative
integer.
[0163] The output signals 31-1, 31-2, . . . , 31-N from the N ITE
microphones 26-1, 26-2, . . . , 26-N are delayed by delays 41-1,
41-2, . . . , 41-N after pre-processing in pre-processors 32-1,
32-2, . . . , 32-N to compensate for the delays of the output
signals 33-1, 33-2, . . . , 33-M from the M BTE microphones 14-1,
14-2, . . . , 14-M, caused by the adaptive cue filters 42-1, 42-2,
. . . , 42-M. The delays 41-1, 41-2, . . . , 41-N may also be used
for beamforming. The output signals 31-1, 31-2, . . . , 31-N from
the N ITE microphones 26-1, 26-2, . . . , 26-N are further combined
in the signal combiner 64, e.g. as a weighted sum, and the output
60 of the signal combiner 64 is fed to a subtractor 72 as in the
circuit shown in FIG. 7.
[0164] Likewise, the output signals 33-1, 33-2, . . . , 33-M from
the M BTE microphones are pre-processed in pre-processors 34-1,
34-2, . . . , 34-M and filtered in the respective adaptive cue
filters 42-1, 42-2, . . . , 42-M and combined in the signal
combiner 50, e.g. as a weighted sum, and the output 52 of the
signal combiner 50 is fed to the subtractor 62 and the hearing aid
processor 18 as in the circuit of FIG. 7.
[0165] The adaptive controller 56 controls the adaptation of the
filter coefficients of adaptive cue filters 42-1, 42-2, . . . ,
42-M to reduce, and preferably eventually minimize, the difference
58 between the output of BTE signal combiner 50 and ITE signal
combiner 64, provided by subtractor 62, e.g. by solving the
minimization problem (2) already mentioned above:
min G 1 ( f , t ) G m ( f , t ) W ( f ) ( ( S IEC ( f , t ) - G 1 (
f , t ) S 1 BTEC ( f , t ) - - G m ( f , t ) S m BTEC ( f , t ) ) p
##EQU00009##
[0166] Wherein S.sup.IEC is the output signal 60 of signal combiner
64, and G.sub.1(f,t), G.sub.2(f,t), . . . , G.sub.n(f,t) are the
transfer functions of the respective adaptive cue filters 42-1,
42-2, . . . , 42-M.
[0167] Typically p=2, and/or W(f)=1.
[0168] Possible weights in the signal combination performed by the
signal combiner 58 are included in the transfer functions
G.sub.1(f,t), G.sub.2(f,t), . . . , G.sub.n(f,t). These weights may
be frequency dependent.
[0169] In this way, the output signal 52 of the BTE signal combiner
50 models the combined ITE microphone audio signal 60 of the ITE
microphones 26-1, 26-2, . . . , 26-N, and thus also substantially
models the HRTFs of the user.
[0170] The new hearing aid circuitry shown in FIG. 9 may operate in
the entire frequency range of the hearing aid 10.
[0171] The hearing aid 10 shown in FIG. 9 may be a multi-channel
hearing aid in which microphone audio signals 31-1, 31-2, . . . ,
31-N, 33-1, 33-2, . . . , 33-M to be processed are divided into a
plurality of frequency channels, and wherein signals are processed
individually in each of the frequency channels.
[0172] For a multi-channel hearing aid 10, FIG. 9 may illustrate
the circuitry and signal processing in a single frequency channel.
The circuitry and signal processing may be duplicated in a
plurality of the frequency channels, e.g. in all of the frequency
channels.
[0173] For example, the signal processing illustrated in FIG. 9 may
be performed in a selected frequency band, e.g. selected during
fitting of the hearing aid to a specific user at a dispenser's
office.
[0174] The selected frequency band may comprise one or more of the
frequency channels, or all of the frequency channels. The selected
frequency band may be fragmented, i.e. the selected frequency band
need not comprise consecutive frequency channels.
[0175] The plurality of frequency channels may include warped
frequency channels, for example all of the frequency channels may
be warped frequency channels.
[0176] Outside the selected frequency band, the at least one ITE
microphone 26-1, 26-2, . . . , 26-N may be connected conventionally
as an input source to the processor 18 of the hearing aid 10 and
may cooperate with the processor 18 of the hearing aid 10 in a
well-known way.
[0177] In this way, the at least one ITE microphone 26-1, 26-2, . .
. , 26-N supply the input to the hearing aid at frequencies where
the hearing aid is capable of supplying the desired gain with this
configuration. In the selected frequency band, wherein the hearing
aid cannot supply the desired gain with this configuration, the
microphones 14-1, 14-2, . . . , 14-M of BTE hearing aid housing are
included in the signal processing as disclosed above. In this way,
the gain can be increased while simultaneously maintain the spatial
information about the sound environment provided by the at least
one ITE microphone.
[0178] In the hearing aid 10 shown in FIG. 10, adaptive feedback
cancellation has been added to the hearing aid shown in FIG. 9
similar to the way illustrated in FIG. 8 in comparison with FIG. 7,
i.e. an adaptive feedback filter 70 is added with an input 72
connected to the output of the hearing aid processor 18 and outputs
74-1, 74-2, . . . , 74-N, 76-1. 76-2, . . . , 76-M connected to
subtractors 78-1, 78-2, . . . , 78-N, 80-1, 80-2, . . . , 80-M for
subtraction of each output from a respective microphone output to
provide a feedback compensated signal 82-1, 82-2, . . . , 82-N,
84-1, 84-2, . . . , 84-M fed to the corresponding pre-processing
circuits 32-1, 32-2, . . . , 32-N, 34-1, 34-2, . . . , 34-M and to
the adaptive feedback filter 70 for control of the adaption of the
adaptive feedback filter 70. The adaptive feedback filter outputs
74-1, 74-2, . . . , 74-N, 76-1. 76-2, . . . , 76-M provide signals
that constitute approximations of corresponding feedback signals
travelling from the output transducer 22 to the respective
microphones 26-1, 26-2, . . . , 26-N, 14-1, 14-2, . . . , 14-M as
is well-known in the art.
[0179] Further, the outputs 76-1, 76-2, . . . , 76-M approximating
feedback signals of the BTE microphones 14-1, 14-2, . . . , 14-M
are connected to the adaptive controller 56 that controls the
filter coefficients of adaptive cue filters 42-1, 42-2, . . . ,
42-M.
[0180] in accordance with, e.g. equation 1 subject to condition 1,
or equation 5, in order to preserve spatial cue and simultaneously
take feedback into account.
[0181] The adaptive controller 56 controls the adaptation of the
filter coefficients of adaptive cue filters 42-1, 42-2, . . . ,
42-M to reduce, and preferably eventually minimize, the difference
58 between the output 60 of the ITE signal combiner 64 and the
output 52 of BTE signal combiner 50, provided by subtractor 62,
e.g. by solving the minimization problem:
Min G 1 BTEC ( f , t ) G n BTEC ( f , t ) W ( f ) ( S IEC ( f , t )
- G 1 BTEC ( f , t ) S 1 BTEC ( f , t ) - - G n ( f , t ) S n BTEC
( f , t ) ) p ( 8 ) ##EQU00010##
subject to the condition that
1 G 1 BTEC ( f , t ) H FB , 1 BTEC ( f ) + + G n BTEC ( f , t ) H
FB , n BTEC 2 .gtoreq. MSG ( f ) or ( 9 ) min G 1 BTEC ( f , t ) G
n BTEC ( f , t ) W ( f ) ( S IEC ( f , t ) - G 1 BTEC ( f , t ) S 1
BTEC ( f , t ) - - G n BTEC ( f , t ) S n BTEC ( f , t ) ) p +
.alpha. G 1 BTEC ( f , t ) H FB , 1 BTEC ( f ) + + G n BTEC ( f , t
) H FB , n BTEC P ( 10 ) ##EQU00011##
wherein S.sup.IEC is the output signal 60 of signal combiner 64,
and G.sub.1(f,t), G.sub.2(f,t), . . . , G.sub.n(f,t) are the
transfer functions of the respective adaptive cue filters 42-1,
42-2, . . . , 42-M.
[0182] Typically p=2, and/or W(f)=1.
[0183] Possible weights in the signal combination performed by the
signal combiner 58 are included in the transfer functions
G.sub.1(f,t), G.sub.2(f,t), . . . , G.sub.n(f,t). These weights may
be frequency dependent.
[0184] In this way, the output signal 52 of the BTE signal combiner
50 models the combined ITE microphone audio signal 60 of the ITE
microphones 26-1, 26-2, . . . , 26-N, and thus also substantially
models the HRTFs of the user.
[0185] The new hearing aid circuitry shown in FIG. 10 may operate
in the entire frequency range of the hearing aid 10.
[0186] Like the hearing aids shown in FIGS. 7-9, the hearing aid 10
shown in FIG. 10 may be a multi-channel hearing aid in which
microphone audio signals 31-1, 31-2, . . . , 31-N, 33-1, 33-2, . .
. , 33-M to be processed are divided into a plurality of frequency
channels, and wherein signals are processed individually in each of
the frequency channels, possibly apart from the adaptive feedback
cancellation circuitry 70, 72, 74-1, 74-2, . . . , 74-N, 76-1,
76-2, . . . , 76-M, 78-1, 78-2, . . . , 78-N, 80-1, 80-2, . . . ,
80-M, 82-1, 82-2, . . . , 82-N, 84-1, 84-2, . . . , 84-M, 86 that
may still operate in the entire frequency range; or, may be divided
into other frequency channels, typically fewer frequency channels
than the remaining illustrated circuitry.
[0187] As in FIGS. 7-9, FIG. 10 may also illustrate the circuitry
and signal processing in a single frequency channel of a
multi-channel hearing aid 10. The circuitry and signal processing
may be duplicated in a plurality of the frequency channels, e.g. in
all of the frequency channels apart from the adaptive circuitry
that may still operate in the entire frequency range; or, may be
divided into its own frequency channels, typically with fewer
frequency channels than the remaining illustrated circuitry.
[0188] For a multi-channel hearing aid 10, the part of FIG. 10
corresponding to the circuitry of FIG. 9 may illustrate the
circuitry and signal processing in a single frequency channel,
while the adaptive circuitry may still operate in the entire
frequency range; or, may be divided into other frequency channels,
typically fewer frequency channels than the remaining illustrated
circuitry.
[0189] The illustrated circuitry and signal processing may be
duplicated in a plurality of the frequency channels, e.g. in all of
the frequency channels.
[0190] For example, the signal processing illustrated in FIG. 10
may be performed in a selected frequency band, e.g. selected during
fitting of the hearing aid to a specific user at a dispenser's
office.
[0191] The selected frequency band may comprise one or more of the
frequency channels, or all of the frequency channels. The selected
frequency band may be fragmented, i.e. the selected frequency band
need not comprise consecutive frequency channels.
[0192] The plurality of frequency channels may include warped
frequency channels, for example all of the frequency channels may
be warped frequency channels.
[0193] Outside the selected frequency band, the at least one ITE
microphone may be connected conventionally as an input source to
the processor 18 of the hearing aid and may cooperate with the
processor 18 of the hearing aid in a well-known way.
[0194] In this way, the at least one ITE microphone 26-1, 26-1, . .
. , 26-N supply the input to the hearing aid at frequencies where
the hearing aid is capable of supplying the desired gain with this
configuration. In the selected frequency band, wherein the hearing
aid cannot supply the desired gain with this configuration, the
microphones of BTE hearing aid housing are included in the signal
processing as disclosed above. In this way, the gain can be
increased while simultaneously maintain the spatial information
about the sound environment provided by the at least one ITE
microphone.
[0195] The hearing aid 10 shown in FIG. 11 is similar to the
hearing aid 10 shown in FIG. 10 and operates in the same way, apart
from the fact that, in FIG. 11, a signal combiner 66 has been
inserted in front of the processor 18. The added signal combiner 66
comprises first filters connected between the processor input and
the output 60 of the signal combiner 64 of the at least one ITE
microphone 26-1, 26-2, . . . , 26-N, and second complementary
filters connected between the processor input and the output 52 of
the signal combiner 50 of the at least one BTE microphone 14-1,
14-2, . . . , 14-M, the filters passing and blocking, respectively,
frequencies in complementary frequency bands so that the output 60
of the signal combiner 64 of the at least one ITE microphone 26-1,
26-2, . . . , 26-N constitutes the main part of the input signal 68
supplied to the processor input in one or more first frequency
bands, and the output 52 of the signal combiner 50 of the at least
one BTE microphone 14-1, 14-2, . . . , 14-M constitutes the main
part of the input signal 68 supplied to the processor input in one
or more complementary second frequency bands.
[0196] In this way, the at least one ITE microphone 26-1, 26-2, . .
. , 26-N may be used as the sole input source to the processor 18
in one or more frequency bands wherein the required gain for
hearing loss compensation can be applied to the output signal 60 of
the at least one ITE microphone 26-1, 26-2, . . . , 26-N. Outside
these one or more frequency bands, the combined output signal 52 of
the at least one BTE sound input transducer 14-1, 14-2, . . . ,
14-M is applied to the processor 18 for provision of the required
gain.
[0197] The combination of the signals performed in signal combiner
66 could e.g. be based on different types of band pass
filtering.
[0198] The hearing aid 10 shown in FIG. 11 may be a multi-channel
hearing aid in which microphone audio signals 31-1, 31-2, . . . ,
31-N, 33-1, 33-2, . . . , 33-M to be processed are divided into a
plurality of frequency channels, and wherein signals are processed
individually in each of the frequency channels possibly apart from
the adaptive feedback cancellation circuitry 70, 72, 74-1, 74-2, .
. . , 74-N, 76-1, 76-2, . . . , 76-M, 78-1, 78-2, . . . , 78-N,
80-1, 80-2, . . . , 80-M, 82-1, 82-2, . . . , 82-N, 84-1, 84-2, . .
. , 84-M, 86 that may still operate in the entire frequency range;
or, may be divided into other frequency channels, typically fewer
frequency channels than the remaining illustrated circuitry. The
signal combiner 66 may connect the audio signal 60 of the at least
one ITE microphone 26-1, 26-2, . . . , 26-N as the sole input
source to the processor 18 in one or more frequency channels in
which no feedback is expected, and the combined output signal 52 of
the at least one BTE sound input transducer 14-1, 14-2, . . . ,
14-M in frequency channels with risk of feedback.
[0199] The hearing aid 10 shown in FIG. 12 is similar to the
hearing aid 10 shown in FIG. 11 and operates in the same way, apart
from the fact that, in FIG. 12, the signal combiner 66 is adaptive,
e.g. so that the interconnections of the output 60 of the signal
combiner 64 of the at least one ITE microphone 26-1, 26-2, . . . ,
26-N and the output 52 of the signal combiner 50 of the at least
one BTE microphone 14-1, 14-2, . . . , 14-M can be changed during
operation of the hearing aid 10, e.g. in response to the status of
the feedback loops, whereby, the at least one ITE microphone 26-1,
26-2, . . . , 26-N may be used as the sole input source to the
processor 18 in one or more frequency bands in which no feedback is
currently present, whereas in one or more frequency bands in which
feedback is evolving, the combined output signal 52 of the at least
one BTE sound input transducer 14-1, 14-2, . . . , 14-M is applied
to the processor 18 for provision of the required gain without
feedback.
[0200] The hearing aid 10 shown in FIG. 12 may be a multi-channel
hearing aid in which microphone audio signals 31-1, 31-2, . . . ,
31-N, 33-1, 33-2, . . . , 33-M to be processed are divided into a
plurality of frequency channels, and wherein signals are processed
individually in each of the frequency channels possibly apart from
the adaptive feedback cancellation circuitry 70, 72, 74-1, 74-2, .
. . , 74-N, 76-1, 76-2, . . . , 76-M, 78-1, 78-2, . . . , 78-N,
80-1, 80-2, . . . , 80-M, 82-1, 82-2, . . . , 82-N, 84-1, 84-2, . .
. , 84-M, 86 that may still operate in the entire frequency range;
or, may be divided into other frequency channels, typically fewer
frequency channels than the remaining illustrated circuitry. The
signal combiner 66 may adaptively connect the audio signal 60 of
the at least one ITE microphone 26-1, 26-2, . . . , 26-N as the
sole input source to the processor 18 in one or more frequency
channels in which no feedback instability is currently present, and
the combined output signal 52 of the at least one BTE sound input
transducer 14-1, 14-2, . . . , 14-M in frequency channels with
current risk of feedback.
[0201] Although particular embodiments have been shown and
described, it will be understood that it is not intended to limit
the claimed inventions to the preferred embodiments, and it will be
obvious to those skilled in the art that various changes and
modifications may be made without departing from the spirit and
scope of the claimed inventions. The specification and drawings
are, accordingly, to be regarded in an illustrative rather than
restrictive sense. The claimed inventions are intended to cover
alternatives, modifications, and equivalents.
* * * * *